1,721,074 research outputs found
SiC Foams Decorated with SnO2 Nanostructures for Room Temperature Gas Sensing
No full textSberveglieri, Giorgio/0000-0003-0080-8117; Ponzoni, Andrea/0000-0001-9955-5118; Comini, Elisabetta/0000-0003-2559-5197; Vakifahmetoglu, Cekdar/0000-0003-1222-4362Cell walls of the commercial silicon carbide (SiC)-based foams were decorated by one-dimensional tin dioxide (SnO2) nanostructures. Thermal evaporation of SnO2 powder with the assistance of a Au catalyst in inert atmosphere caused the formation of SnO2 nanobelts on the pore surfaces. The room temperature (RT) ammonia (NH3) and nitrogen dioxide (NO2) gas sensing behaviors were investigated systematically in both dry and humid air atmosphere with/without UV activation. The results were compared to those for bare SnO2 and SiC. It was shown that SiC/SnO2 composite was efficient to detect low concentration of NH3 (10-50 ppm) and NO2 (1-5 ppm) under humid air and UV activation at RT.TUBITAK (The Scientific and Technological Research Council of Turkey)Turkiye Bilimsel ve Teknolojik Arastirma Kurumu (TUBITAK) [CAYDAG-113Y533]The author wishes to express sincere appreciation to Prof. Gian Domenico Soraru and his team in University of Trento for the N2 adsorption and desorption data. C. V. gratefully acknowledge the support of TUBITAK (The Scientific and Technological Research Council of Turkey) under the project Grant No. CAYDAG-113Y533
Gas sensing characteristics of Fe-doped tungsten oxide thin films
No full textThis study reports on the gas sensing characteristics of Fe-doped (10 at.%) tungsten oxide thin films of various thicknesses (100-500 nm) prepared by electron beam evaporation. The performance of these flims in sensing four gases (H-2, NH3, NO2 and N2O) in the concentration range 2-10,000 ppm at operating temperatures of 150-280 degrees C has been investigated. The results are compared with the sensing performance of a pure WO3 film of thickness 300 nm produced by the same method. Doping of the tungsten oxide film with 10 at.% Fe significantly increases the base conductance of the pure film but decreases the gas sensing response. The maximum response measured in this experiment, represented by the relative change in resistance when exposed to a gas, was Delta R/R=375. This was the response amplitude measured in the presence of 5 ppm NO2 at an operating temperature of 250 degrees C using a 400 nm thick WO3 :Fe film. This value is slightly lower than the corresponding result obtained using the pure WO3 film (Delta R/R = 450). However it was noted that the WO3:Fe sensor is highly selective to NO2. exhibiting a much higher response to NO2 compared to the other gases. The high performance of the sensors to NO2 was attributed to the small grain size and high porosity of the films, which was obtained through e-beam evaporation and post-deposition heat treatment of the films at 300 degrees C for 1 h in air. (C) 2012 Elsevier B.V. All rights reserved
Nanostructured WO3 deposited by modified thermal evaporation for gas-sensing applications
No full textIn this work, we present a simple method, based on a modified thermal evaporation technique, to obtain films of nanostructured WO3 with high surface roughness. This method consists on sublimation from a metallic tungsten wire followed by oxidation in low vacuum conditions and reactive atmosphere ((PO2)=0.22 mbar), with substrates heated at high temperature (600 degrees C). Electron microscopy (SEM, TEM) and atomic force microscopy (AFM) analysis revealed that the deposited films are composed of agglomerates with nanometric size and present high surface roughness and large effective area suitable for gas-sensing applications. Sensing measurements highlighted promising performances, particularly at the working temperature of 100 degrees C: high responses towards sub-ppm concentrations of NO2 have been observed compared to the lower ones observed for NH3 and CO. NO2 tests performed with sensors based on sputtered thin films highlighted that sensors obtained by this thermal evaporation like method exhibit improved performances. (c) 2005 Elsevier B.V. All rights reserved
Copper oxide nanowires for surface ionization based gas sensor
No full textThis work focuses on the development of surface ionization gas sensors based on copper oxide (CuO). CuO nanowires were prepared by thermal oxidation starting from a thin film of metallic copper deposited by RF magnetron sputtering. In addition to the well-known conductimetric sensors, we have developed another kind of device depending upon a different sensing mechanism, namely surface ionization (SI). SI phenomenon involves ions formed by the adsorption of gas molecules on heated solid surface, the electron transfer from the adsorbed species to the electrode surface and the extraction of the ion adsorbates into free space by an external electrical field. Our preliminary results show that humidity plays an important role in the ions formation and so in sensors performance. For this reason we have done a systematic study on the interaction mechanism of target molecules with hydroxyl groups adsorbates on CuO surface, explaining the experimental results in terms of acidity/basicity
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